The present invention relates to a wavelength conversion laser which can generate a sum frequency laser beam of high output power and high focusibility in a stable manner with high reproducibility, and a laser machining device.
FIG. 15 is a schematic view showing a construction of a conventional wavelength conversion laser, for example, shown in Japanese Laid-Open Patent Application No. 148096/1975 (Tokukaishou 50-148096). In FIG. 15, reference numeral 1 is a laser resonator mirror having a high reflectivity with respect to a fundamental laser beam, 3 is a solid-state laser active medium, 6c is a second harmonic generation wavelength conversion crystal, 7c is a sum frequency generation (third harmonic generation) conversion crystal, 9 is a laser resonator mirror, having a high reflectivity with respect to the second harmonic laser beam and the fundamental laser beam, and 18 is a mirror which has a high reflectivity to the fundamental laser beam and also has a high transmittance to the second harmonic and sum frequency laser beam.
In the wavelength conversion laser shown in FIG. 15, a fundamental laser beam, generated by a laser resonator consists of the laser resonator mirrors 1, 9 and the mirror 18 and the solid-state laser active medium 3, is partially converted into a second harmonic laser beam by the second harmonic generation wavelength conversion crystal 6c placed inside the laser resonator, and one portion of the second harmonic laser beam thus generated and one portion of the fundamental laser beam are converted into a third harmonic laser beam serving as a sum frequency laser beam by the sum frequency generation wavelength conversion crystal 7c. The second harmonic laser beam (2xcfx89) that has not been wavelength-converted and the third harmonic laser beam (3xcfx89) are extracted from the mirror 18. In the wavelength conversion laser as described above that inserts the sum frequency generation wavelength conversion crystal and the second harmonic generation wavelength conversion crystal into the laser resonator so as to generate the sum frequency laser beam, the output of the sum frequency laser beam is maximized by alternately adjusting the angle and temperature of the respective wavelength conversion crystals.
In case when as shown in FIG. 15, the wavelength conversion laser for generating the sum frequency laser beam is constructed by inserting the second harmonic generation wavelength conversion crystal and the sum frequency generation wavelength conversion crystal into the laser resonator. However, the wavelength conversion efficiency varies depending on the angle of the wavelength conversion crystal and the temperature, with the result that the characteristics of the fundamental laser beam within the laser resonator also vary; therefore, it is difficult to construct such a device with high reproducibility. The complexity and difficulty in constructing such a device is far greater than those in constructing a fundamental laser beam generation device and those in constructing a second harmonic laser beam generation device, having only one wavelength conversion crystal inside the laser resonator. Moreover, Patent Gazette No. 2654728, etc. also disclose wavelength conversion lasers in which a wavelength conversion crystal is placed inside the laser resonator; however, like those shown in FIG. 15, it is difficult to provide a device with high reproducibility even by the application of these devices.
The above-mentioned complexity in the output power variation of the wavelength conversion laser that depends on the angle and the temperature of the wavelength conversion crystals and obstacles that are inevitable in manufacturing the devices, such as variations in parts and differences in the capability of individual workers, have made it difficult to manufacture and mass-produce wavelength conversion lasers in factories, etc. Moreover, complex working processes, which are required for production and maintenance for the device, have made the production costs higher. Furthermore, skilled workers are required.
In case when a laser beam, generated by the above-mentioned wavelength conversion laser, is used for machining, if a constituent part of the laser (such as a semiconductor laser and a lamp for a pumping light source, a wavelength conversion crystal and an optical part such as a mirror) is damaged and an exchange is required, time-consuming adjustments have to be carried out on the optical system and the resonator, and it is sometimes difficult to reproduce the same machining result as before the repairing even in case of machining under the same operation conditions, since the laser does not reproduce the same state as before the repairing.
The wavelength conversion laser in accordance with claim 1 of the present invention, which is a wavelength conversion laser for obtaining a sum frequency laser beam by placing a second harmonic generation wavelength generation conversion crystal and a sum frequency generation wavelength conversion crystal inside a laser resonator, is characterized in that the second harmonic generation wavelength conversion crystal that is shorter than the sum frequency generation wavelength conversion crystal is adopted.
Moreover, the laser in accordance with claim 2, which is the same laser as claim 1, is characterized in that the sum frequency generation wavelength conversion crystal serves as a third harmonic generation wavelength conversion crystal.
Furthermore, the laser in accordance with claim 3, which is the same wavelength conversion laser as claim 1, is characterized in that the sum frequency generation wavelength conversion crystal is made of a plurality of wavelength conversion crystals.
The laser in accordance with claim 4, which is the same wavelength conversion laser as claim 3, is characterized in that the sum frequency generation wavelength conversion crystals are two wavelength conversion crystals so as to generate fourth harmonic laser beam.
Moreover, the laser in accordance with claim 5, which is the same wavelength conversion laser device as claim 1, is characterized in that the sum frequency generation wavelength conversion crystal is placed between the solid-state laser active medium and the second harmonic generation wavelength conversion crystal.
Furthermore, the laser in accordance with claim 6, which is the same wavelength conversion laser as claim 1, is characterized in that a resonator Q-value modulating element is placed inside a laser resonator.
The laser in accordance with claim 7, which is the same wavelength conversion laser as claim 1, is characterized in that a device, which can finely adjust the angle of at least one of the wavelength conversion crystals with a precision of not more than xc2x10.1 degree, is installed.
Moreover, the laser in accordance with claim 8, which is the same wavelength conversion laser as claim 1, is characterized in that a device, which can finely adjust the temperature of at least one of the wavelength conversion crystals with a precision of not more than xc2x10.5 degree centigrade, is installed.
Furthermore, the laser in accordance with claim 9, which is the same wavelength conversion laser as claim 1, is characterized in that a polarization controlling element is placed inside the laser resonator.
The laser in accordance with claim 10, which is the same wavelength conversion laser as claim 1, is characterized in that Nd:YAG or Nd:YLF or Nd:YVO4 is used as the solid-state laser active medium.
The laser in accordance with claim 11, which is the same wavelength conversion laser as claim 1, is characterized in that LBO (LiB3O5) crystal is used at least either as the second harmonic generation wavelength conversion crystal or as the sum frequency generation wavelength conversion crystal.
Moreover, the laser in accordance with claim 12, which is the same wavelength conversion laser as claim 1, is characterized in that the sum frequency laser beam average output power is not less than 1 W.
Furthermore, the laser in accordance with claim 13, which is the same wavelength conversion laser as claim 1, is characterized in that the second harmonic generation wavelength conversion crystal and the sum frequency generation wavelength conversion crystal are formed into an integrated wavelength conversion element so as to integrally vary the temperature or angle of the second harmonic generation wavelength conversion crystal and the sum frequency generation wavelength conversion crystal.
The machining device in accordance with claim 14 is a laser machining device for machining a machining object by using a wavelength conversion laser beam generated by the wavelength conversion laser disclosed in claim 1 as a light source.